The present invention relates to leached fiber bundles (LFBs) which are used in endoscopes and for optical signal communications, and more particularly, to improved methods of producing such LFBs with higher quality and reliability.
It has been previously known to produce image conductors or guides for endoscopes or for transmitting optical signals in the form of LFBs. Such LFBs include a large number of optical fibers, which may be arranged in an ordered array, with each fiber having a small diameter, for example 10-100 microns. The LFBs may be formed by drawing a fiber bundle preform having a number of pre-arranged optic fiber preforms, in the form of glass rods and/or tubes, together with at least some leachable glass spacers located between or encapsulating each of the desired optic fiber preforms. The fiber bundle preform is drawn down to the desired size for the optical fibers, which are fused together with the leachable glass spacers as they are drawn, with the leachable glass spacers maintaining a space between the individual optic fibers. In order to form a flexible image guide, the ends of the fused optical fiber bundle are protected with a soft, etch resistant coating, and the leachable glass from the spacers is leached from the fused optical fiber bundle, typically using an acid etch bath. Once the leaching process is complete, the individual optical fibers in the middle portion of the leached optical fiber bundle are free and allow the LFB to be flexed, while the ends are still held together. Ferrules are then installed on the ends to protect the ends from damage and maintain the fibers in position. The flexible middle portion may be placed within a flexible outer sheath to prevent the individual optical fibers from being damaged.
There are several problems with this prior known process. Due to the small size of the optic fibers, the individual fibers in the LFB are extremely sensitive to outside surface damage and breakage during handling, such as during removal from the etch bath and further processing, such as the installation of the end ferrules. This creates an additional expense due to the special handling required for such further operations. The optic fibers of the LFB can also suffer from damage or breakage during use in the final product or application, for example in a flexible endoscope, due to friction and abrasion between adjacent fibers as the middle, flexible portion of the LFB is flexed. This results in a loss of image definition and degradation of transmission capability. It would be advantageous to reduce the possibility of such optical fiber damage during the formation of the LFB and in the subsequent handling and production of the final product in which the LFB is utilized. It would also be advantageous to reduce production cost and provide a longer useful life for LFBs.